Electrically actuated incremental valves suitable for use as expansion valves in refrigeration or air conditioning systems are typically comprised of two types. The first type typically includes a solenoid connected to an appropriate electrical supply which, in response to a pulsed electrical signal, actuates a plunger or control element alternately into and out of a flow path through the expansion valve body to permit or prevent fluid flow. The second type of electrically actuated expansion valve has a rotary actuator with a means for converting the rotary motion into linear motion for operating a valve element to increase or decrease the flow area available through the valve body by seating against a valve seat to close the valve and prevent flow or moving linearly away from the valve seat to permit flow through an area defined by the area of the opening between the valve element and the valve seat. There are disadvantages associated with both types of electrically actuated valves which have been found difficult to overcome in the prior art.
The solenoid actuated expansion valves tend to cycle between completely open and completely closed, cycling at rate in the range of fractions of hertz to hundreds or thousands of hertz. Thus these valves often suffer from a shortened life span due to component fatigue and wear induced by the high cycle rate and corresponding speed and frequency of component movement required to maintain relatively smooth fluid flow through the refrigeration system. In addition, these valves, due to the open-closed cycle action; cause a pulsation in the fluid flow through the expansion valve body, often inducing stress and related failures of other components in the refrigeration system in which they are employed. Furthermore, the solenoid actuated expansion valves are susceptible to damage or even failure due to debris or foreign matter flowing through the refrigeration system coming into contact with the valve components during operation of the valve. Therefore, many have turned to the rotary actuated expansion valve.
The typical rotary actuated expansion valve is operated by a rotary stepping motor providing incremental rotary motion which is translated then to incremental linear motion to actuate a valve element in a linear axial fashion. Typically, the valve element is driven against the valve seat to sealingly cover an aperture, preventing fluid flow therethrough and closing the valve or alternatively is driven away from the seat to open the valve. The distance of the valve element from the valve seat determines the flow area available through the valve up to a maximum determined by the area of the aperture of the valve seat. Alternatively, in a second type of rotary expansion valve, the valve element may be a member which is driven to cover or uncover the inlet or outlet orifice in a line normal to the flow through the valve body. In this type of rotary actuated valve, the flow is determined by the amount of area of the flow orifice which is uncovered at any given time by the valve element.
These typical rotary actuated expansion valves have a tendency to stick, due to friction and the viscosity of contaminants collected upon the valve body. Overcoming this tendency to stick requires oversized, costlier motors and concurrently decreases the controllability of the system. This decrease in controllability results from the fact that the rotary actuator may fail to overcome the sticking of the valve element for one or more actuating pulses or steps, therefore causing the valve element to be improperly positioned. The controller for the valve, having sent a specified number of pulses intended to actuate the valve to a desired opening, will in fact have actuated the valve to a smaller degree than calculated or desired. The system then indicates the need for further opening of the valve, and the controller will begin to "hunt" for the appropriate setting of the valve.
This second type of rotary actuated expansion valve also typically is comprised of many relatively small parts which must be machined to close tolerances to prevent fluid leakage through the valve and to improve operating characteristics. However, such close tolerance machining is often expensive and time-consuming, as is the assembly of valves containing such parts. Furthermore, the second type of rotary actuated expansion valve often includes a relatively large number of elastomeric seals to prevent flow from bypassing the valve element, as well as one or more springs having a large traverse distance, all of which are susceptible to wear and breakage. These items tend to substantially decrease the reliability of the valve in that wear can cause leakage through the valve and sticking of the valve, with a corresponding loss of control and efficiency of the system in which the valve is applied, as well as increased maintenance and downtime costs.
It is an object of the present invention to provide a rotary actuated valve of simple construction.
It is a further object of the present invention to provide a rotary actuated valve which is highly reliable, with low maintenance requirements and costs.
It is yet another object of the invention to provide such a valve which is susceptible of mass production.
It is yet another object of the invention to provide such a valve which is relatively immune to the effects of foreign matter or debris flowing through the valve.
It is yet another object of the present invention to provide such a valve as will appropriately respond to a controller input to permit a smooth, pulse-free fluid flow through the valve.
It is yet another object of the invention to provide such a valve which is suitable specifically for such applications as an expansion valve in a refrigeration system.
These and other objects of the present invention will be apparent from the attached drawings and the description of the preferred embodiment that follows hereinbelow.